Amyotrophic Lateral Sclerosis (ALS or Lou Gherig's disease) is an adult onset motor neuron disease characterized by progressive loss of motor function and death from respiratory insufficiency, usually within five years of diagnosis. No adequate treatment exists. Most cases of ALS are sporadic;however, several genetic loci have been linked to familial forms of the disease, the most common (fALS1) being dominantly inherited mutations in the gene encoding Cu/Zn-superoxide dismutase (SOD1). Experimental models of fALS1 are used in preclinical testing of compounds for eventual use in treating sporadic as well as familial ALS. Given that ALS can be caused by multiple, mostly unidentified insults, common mechanisms of disease progression and general neuroprotective pathways are targets for intervention. Objective/Hypothesis: The long term objective is to develop a therapy for ALS and other motor neuron disorders based on a novel series of compounds that inhibit Hsp90, a heat shock protein (HSP) that plays a pivotal role in regulating folding and turnover of proteins with aberrant conformation. The underlying hypothesis is that these compounds will be efficacious through two mechanisms that contribute to protein quality control: (1) upregulating multiple heat shock proteins (HSPs) with protein chaperoning and refolding function, thereby preventing damaged proteins (arising from genetic mutation or epigenetic modification) from adopting toxic conformations and aggregating, and (2) promoting degradation of Hsp90 client proteins, including mutant and misfolded proteins, thereby reducing the toxic burden. The short term objective is to evaluate our presumptive lead compound, NXD30001 in primary tissue culture models and a transgenic mouse model of fALS. The realization of our goals will help further the mission of the NINDS, to reduce the burden of neurologic disease. Specific Aim 1: To test NXD30001 in existing in vitro primary culture models of ALS. Test-models are established by (1) expressing ALS-causing mutant SOD1 proteins in motor neurons of dissociated cultures of embryonic murine spinal cord-dorsal root ganglia (DRG), and (2) preparing spinal cord-DRG cultures from mutant SOD1 transgenic mouse embryos. These experiments will establish bioactivity of NXD30001 in motor neurons, specifically expression of HSPs and increased turnover of Hsp90 client proteins, and will evaluate the effectiveness of NXD30001 in preventing toxicity of fALS-causing SOD1 mutants. Specific Aim 2. Perform proof-of-concept studies in an fALS animal model to determine the in vivo utility of the NXD30001 compound. The efficacy of NXD30001 will be assessed in transgenic mice expressing the disease-causing SOD1 mutant, SOD1G93A. Two dosage regimens will be evaluated for delaying onset and progression of motor neuron disease, using induction of HSPs and reduction in levels of of Hsp90 client proteins as markers of NXD30001 bioactivity in brain and spinal cord. PUBLIC HEALTH RELEVANCE: The only approved drug for treating Amyotrophic Lateral Sclerosis (ALS), riluzole, provides minimal benefit for this fatal disease. With an incidence of 1-2 per 100,000, ALS represents a serious unmet medical need, which will only grow as the population ages. The proposed research may provide proof-of-principle evidence for the inhibition of heat shock protein 90 (Hsp90) as a potential approach for treating ALS, and will likely accelerate the process of discovery and development of novel therapeutics for ALS and other motor neuron disorders.